Standard Wireline Data Processing
IODP logging
contractor: USIO/LDEO
Hole: U1330A
Expedition: 320T (sea trials)
Location: Ontong-Java Plateau (Equatorial NW Pacific)
Latitude: 3° 36.3498' N
Longitude: 156° 37.4417' E
Sea floor
depth (driller's):
2816 mbrf
Sea floor
depth (logger's): 2812 mbrf
Total
penetration: 553.8 mbsf (3369.8 mbrf)f
Total core
recovered: 16.16 m (84 % of cored section)
Oldest
sediment recovered: early Pliocene
Lithologies: white nannofossil ooze with foraminifers.
The logging data
was recorded by Schlumberger in DLIS format. Data were processed at the
Borehole Research Group of the Lamont-Doherty Earth Observatory in February 2009.
Tool string | Pass |
Top depth (mbsf) |
Bottom depth (mbsf) |
Pipe depth (mbsf) |
Notes |
DIT/HLDS/GPIT/HNGS
|
Downlog
|
0 |
518 |
99 |
No source on HLDS
|
DIT/HLDS/GPIT/HNGS
|
Main
|
0 |
555 |
96 |
No source on HLDS
|
DIT/HLDS/GPIT/HNGS |
Repeat
|
450 |
555 |
No source on HLDS |
|
FMS/GPIT/HNGS |
Pass 1
|
137 |
525 |
||
FMS/GPIT/HNGS |
Pass 2
|
137 |
520 |
||
MSS/HLDS/GPIT/HNGS
|
Main |
97.5 |
469 |
No source on HLDS |
|
MSS/HLDS/GPIT/HNGS |
Repeat 1 |
277 |
475
|
No source on HLDS |
|
MSS/HLDS/GPIT/HNGS
|
Repeat 2
|
583 |
473 |
No source on HLDS. Caliper closed. |
Logging opeartions started with the DIT/HLDS/GPIT/HNGS string which recorded data downlog first and then uplog on a main and repeat run. During the repeat the wireline winch experienced some technical difficulties which eventually required the closing of the caliper from 3335 to 3280 mbrf (523-468 mbsf) to prevent possible damage. No problems were encountered during the main run of the DIT/HLDS/GPIT/HNGS string. The FMS/GPIT/HNGS tool string encountered significant bridges, which prevented it from reaching total depth.
The new MSS sonde was run three times, delivering a main run and two repeat sections. The caliper was kept open during the first reapeat and closed during the second one.
The WHC was used and tested throughout logging operations.
The depths in
the table are for the processed logs (after depth shift to the sea floor and depth matching between passes). Generally, discrepancies may exist between the
sea floor depths determined from the downhole logs and those determined by the
drillers from the pipe length. Typical reasons for depth discrepancies are ship
heave, wireline and pipe stretch, tides, and the difficulty of getting an
accurate sea floor from a 'bottom felt' depth in soft sediment.
Depth shift to sea floor and depth match. The original logs were first shifted to the sea floor (- 2812 m). The sea floor depth was determined by the step in gamma ray values at 2812 mbrf on the DIT/HLDS/GPIT/HNGS logs . This differs by 4 m from the sea floor depth given by the drillers (2816 mbrf). Then the depth-shifted DIT/HLDS/GPIT/HNGS main run has been depth-matched to the first pass of the FMS/GPIT/HNGS tool string using the caliper log, because of the low signature and poor correlation of the gamma ray logs. For the same reason, the DIT/HLDS/GPIT/HNGS downlog has been depth-matched to the main run using the resistivity logs. Neither the FMS/GPIT/HNGS Pass 2 or the repeat of the DIT/HLDS/GPIT/HNGS logs needed depth-matching. The main run of the MSS/HLDS/GPIT/HNGS was depth-matched to the reference FMS/GPIT/HNGS using the caliper logs. The two repeats of the MSS were then matched to the main MSS using the susceptibility curves (low resolution sensor).
Depth matching
is typically done in the following way. One log is chosen as reference (base)
log (usually the total gamma ray log from the run with the greatest vertical
extent and no sudden changes in cable speed), and then the features in the
equivalent logs from the other runs are matched to it in turn. This matching is
performed manually. The depth adjustments that were required to bring the match
log in line with the base log are then applied to all the other logs from the
same tool string.
Environmental corrections. The HNGS was corrected for hole size during the recording.
Magnetic susceptibility data. The magnetic susceptibility toold was run for the first time during Expedition 320T. At the time of this processing the recorded data has not been calibrated yet and therefore is not presented in ASCII file format in the online database. It will be included at a later date.
The quality of
the data is assessed by checking against reasonable values for the logged
lithologies, by repeatability between different passes of the same tool, and by
correspondence between logs affected by the same formation property (e.g. the
resistivity log should show similar features to the sonic velocity log).
The good correlation between the different runs suggests that the wireline heave compensator performed well.
Despite the lack of calibration of the susceptibility log, there is good correlation between the three passes. More processing in required to produce final results.
Gamma ray logs
recorded through bottom hole assembly (BHA) and drill pipe should be used only
qualitatively, because of the attenuation of the incoming signal. The
thick-walled BHA attenuates the signal more than the thinner-walled drill pipe.
Hole diameter was recorded by the hydraulic caliper on the HLDS tool (LCAL) and by the FMS tool (C1 and C2). The caliper was closed from 3335 to 3280 mbrf (523-468 mbsf) during the DIT/HLDS/GPIT/HNGS downlog and repeat run and during the MSS/HLDS/GPIT/HNGS second repeat run.
A null value of
-999.25 may replace invalid log values.
Additional
information about the drilling and logging operations can be found in the
Operations and Downhole Measurements sections of the expedition reports,
Proceedings of the Integrated Drilling Program, Expedition .
For further questions about the logs, please contact:
Cristina Broglia
Phone: 845-365-8343
Fax: 845-365-3182
E-mail: Cristina Broglia